Toilet tanks have a flapper valve, which is pulled into an open position by the flush mechanism. Once the flapper valve is in the open position, water flows from the toilet tank into the toilet bowl. Most devices intended to conserve water in a toilet cause the flapper valve to close before all of the water has been drained from the toilet tank. The differences between the mechanisms involve the manner in which they act upon the flapper valve. One group of patents; such as U.S. Pat. No. 4,945,578 exert a force on top of the flapper valve to push it to a closed position. Another group of patents, such as U.S. Pat. No. 5,341,522, pull the flapper valve into the closed position.
As this class of water conservation devices has evolved they have gradually decreased in complexity and cost, while increasing in effectiveness and ease of installation.